Solutions have long been sought to reduce the deleterious effects of air pollution caused by byproducts resulting from the high-temperature imperfect combustion of organic materials. When combustion occurs in the presence of excess air and at high temperatures, harmful byproducts, such as nitrogen oxides (NOx), are created. NOx plays a major role in the formation of ground-level ozone that is associated with asthma and other respiratory ailments. NOx also contributes to soot, linked to a number of serious health effects, as well as acid rain and the deterioration of coastal estuaries. As a result, NOx emissions are subject to many regulatory provisions limiting the amount of NOx that may be present in effluent gas vented into the surrounding environment.
One known solution involves the use of selective catalytic reduction (SCR) to reduce NOx to nitrogen gas (N2) using ammonia (NH3) as a reductant. However, as ammonia's own hazardous consequences become better known, the use of NH3 in a SCR system presents additional environmental and other problems that must also be addressed.
As regulatory agencies continue to drive limits on NOx emission lower, other regulations are also driving down the permissible levels of NH3 that may be emitted into the atmosphere.